Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and the ink sticks are pushed or slid along the feed channel by a feed mechanism and/or gravity toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium.
One difficulty faced in solid ink technology is differentiation and identification of ink sticks to ensure the correct loading and compatibility of an ink stick with the imaging device in which it is used. Provisions have been made to ensure that an ink stick is correctly loaded into the intended feed channel and to ensure that the ink stick is compatible with that printer. One such provision is directed toward physically excluding wrong colored or incompatible ink sticks from being inserted into the feed channels of the printer. For example, the correct loading of ink sticks has been accomplished by incorporating keying, alignment and orientation features into the exterior surface of an ink stick. These features are protuberances or indentations that are located in different positions on an ink stick. Corresponding keys or guide elements in the ink loader of the phase change ink printer exclude ink sticks which do not have the appropriate perimeter key elements while ensuring that the ink stick is properly aligned and oriented in the feed channel.
World markets with various pricing and color table preferences, however, have created a situation where multiple ink types may exist in the market simultaneously with nearly identical size/shape ink and/or ink packaging. Thus, ink sticks may appear to be substantially the same but, in fact, may be intended for different phase change printing systems due to factors such as, for example, market pricing or color table. Due to the broad range of possible ink stick configurations, marketing strategies, pricing, etc., differentiating the inks sticks so only appropriate ink is accepted by a printer requires methods of identification that go beyond physical keying.
In response to the identification requirements posed by the broad range of ink stick configurations, ink sticks have been developed that include sensor features. Sensor features comprise one or more features formed into the exterior surface of ink sticks that are configured to interact with sensors in the ink delivery system. Ink stick data may be encoded into these features by configuring the features to actuate one or more sensors in an ink loader to generate a signal or coded pattern of signals that corresponds to information specific to the ink stick. The ink stick data encoded onto the ink stick may be read by the print controller in a suitably equipped phase change ink jet printing device to control imaging operations. For example, the controller may enable or disable operations, optimize operations or influence or set operation parameters based on the ink stick data encoded onto the ink stick.
Reading an encoded sensor feature incorporated into an ink stick typically requires moving or transporting an ink stick past the appropriate sensor in the feed channel. Ink stick movement in the feed channel generally corresponds to the melt rate of ink sticks at the heater plate. Melt cycles are only performed as needed by the printer. Therefore, when a melt cycle is not being performed, ink sticks may remain stationary in the feed channel. Ink stick movement may also be in response to a loading motion in which a loaded ink stick is “pushed” into contact with ink sticks already loaded into the feed channel at which point it is moved at the melt rate along with the other ink sticks. These variations in movement rate of ink sticks and the timing in which ink sticks interact with the sensors in the feed channel increases the likelihood of incorrect sensing or reading of the encoding feature.